The pancreas is an organ that has endocrine (islet lineage) and exocrine compartments (acinar and ductal lineage). The ductal tree consists of terminal, or intercalated, ducts that interface with acini or centroacinar cells, which are potentil sites of progenitor cells. Intercalated ducts merge to form intralobular ducts, and these in turn merge to form interlobular ducts, and finally, into the main duct that traverses the pancreas to the duodenum, delivering fluid laden with digestive enzymes. We have emphasized studies (in the previous cycle) on the governance of the regulation of ductal branching morphogenesis. Using this as a platform, we now wish to elucidate the transcriptional programs that regulat ductal development, but in particular regulate the emergence of ductal structures during acinar-ductal metaplasia (ADM) and the transition of normal ducts to preneoplastic ducts (termed PanIN). We hypothesize that a newly discovered homeodomain transcription factor, Prrx-1, is critical in ductal cell morphogenesis, acinar-ductal metaplasia, and re-neoplasia. This hypothesis will be pursued by the following Specific Aims through complementary in vitro and rigorous in vivo approaches: (1) To elucidate the mechanistic underpinnings of Prrx1 in ADM and PanIN. We will determine the functional roles of Prrx1+ cells in ADM through genetic lineage tracing studies in vivo. We will define the dependence of pancreatic regeneration after ADM through the pancreatic conditional knockout of Prrx1. We will determine if Prrx1+ cells are more susceptible to the effects of oncogenic KrasG12D in the development of PanIN. (2) To determine the gene targets of Prrx1 through CHiP-Seq, to validate specific gene targets identified in preliminary analysis and determine their functiona relationships. (3) To delineate the functional differences between Prrx1 isoforms in the roles in ADM and PanIN: the role of Prrx1b in self-renewal of cells and role of Prrx1a in invasion. Our novel insights and innovative approaches will for the first time help to mechanistically characterize a transcriptional factor that is critical in ductal development, ADM and PanIN, and place this gene as potentially as important as Pdx1 in the endocrine lineage and Ptf1a (p48) in the acinar lineage. These studies will help to provide opportunities for management of pancreatitis to enhance tissue regeneration and of PanIN/PDAC.